The present invention relates to a work machine comprising a front section with a front frame and a first set of ground engaging members, a rear section with a rear frame and a second set of ground engaging members, and at least one pivot joint between the front section and the rear section allowing the front section to pivot with regard to the rear section, wherein one of the front section and the rear section comprises a power source.
The invention will below be described for an articulated hauler. This should however be regarded as a non-limiting example, wherein the invention may be realized in other types of articulated work machines, such as wheel loaders. Further terms frequently used for work machines are “earth-moving machinery”, “off-road work machines”, “construction equipment” and “forest machines”. The term “ground engaging members” may comprise wheels, caterpillar tracks etc.
In connection with transportation of heavy loads, e.g. in contracting work, a work machine of the type of an articulated hauler is frequently used. Such vehicles may be operated with large and heavy loads in areas where there are no roads, for example for transports in connection with road or tunnel building, sand pits, mines, forestry and similar environments. Thus, an articulated hauler is frequently used in rough terrain with various slippery ground.
The front frame carries a power source in the form of an internal combustion engine and a load-carrying container is arranged on the rear frame of an articulated hauler. An articulated hauler is further defined by a first pivot joint arranged to allow the front frame and the rear frame to pivot in relation to each other around an imaginary longitudinal axis, that is an axis that runs in the longitudinal direction of the vehicle. Travelling on uneven ground is substantially improved by virtue of such a joint.
The articulated hauler further has a second, vertical pivot joint between the front frame and the rear frame and a pair of hydraulic cylinders for steering the work machine via pivoting the front frame relative to the rear frame about the vertical pivot axis. It is emphasized that a frame-steered work machine is adapted for an optimized off road performance with regard to any vehicle with Ackerman steering (front wheel steering). More specifically, the articulated steering creates conditions for using much larger (both with regard to diameter and width) front wheels than with so-called Ackermann steering. Further, articulated steering creates conditions for 100% lock in the front axle differential (which is not possible with Ackermann steering), which is essential when operating on slippery ground.
Further, an articulated hauler normally has six wheels. The front section comprises a front wheel axle and the rear section comprises a pair of bogie axles. A powertrain is adapted to drive the three wheel axles. Thus, the articulated hauler may be operated with all (6) wheel drive. Alternatively, an articulated hauler may be provided with eight wheels, wherein the front section carries four wheels.
Each axle is provided with a differential gear and a (transverse) differential lock. Further, one longitudinal differential lock is provided on the transmission shaft between the front axle and the bogie axles and a further longitudinal differential lock is provided on the transmission shaft between the bogie axles. The differential locks are preferably engaged when there is a risk of the wheels slipping. According to an alternative design, any of the differential locks may be replaced by a device allowing limited slip.
A conventional articulated hauler features a longitudinally installed diesel engine with a gearbox and a dropbox in line. Further, there may be some interconnecting shafts. There is a considerable interference between such an installation and the operating envelope of the front axle as well as the operator/cab connected to this layout.
Further, a specific torque distribution between the front and rear wheels has to be chosen and set during design due to the characteristics of the mechanical powertrain of the articulated hauler. Thus, the specific torque distribution can only be optimized for one specific situation.
Thus, articulated haulers are traditionally equipped with diesel engines and mechanical transmissions. It is also known with hydrostatic drive haulers, but they are generally known by heavier fuel consumption and thereby increased emissions.
Due to future decrease in oil production and more stringent emission regulations, lower fuel consumption and thereby associated lower emission impact are two of the most important features for all future machines and vessels in any branch all over the world.
It is desirable to achieve an articulated work machine, which is energy efficient in operation and which creates conditions for an improved operation.
According to an aspect of the present invention, the other of the front section and the rear section comprises at least one electric motor adapted for driving at least one of said ground engaging members.
Thus, an aspect of the invention is particularly directed to a hybrid electric work machine.
According to an aspect of the invention, in an articulated hauler, the power source is preferably arranged in the front section and the electric motor is arranged in the rear section. Thus, the front section forms a pull unit. Further, the front section comprises a cab and the rear section comprises a load-carrying container.
The electric motor creates conditions for an infinitely variable torque distribution between the wheels which is advantageous when operating in severe terrain conditions.
Regarding an articulated hauler, an aspect of the invention creates conditions for an improved performance with regard to cornering. More specifically, according to prior art, the front wheel axle and the rear wheel axles have substantially different turning radius, which may give rise to constrained torque in the mechanical powertrain from the engine to the wheels concerned. According to an aspect of the invention, since the rear wheels are driven via electrical motor(s), the mechanical transmission of power to the rear wheels may be eliminated, wherein the powertrain problems due to different turning radius are relieved. Thus, the rotation speed of the front wheel axle in relation to the bogie axles can be adjusted during cornering.
Further, the need for a mechanical transmission of motive power (comprising dropbox, propeller shafts and rear axles with final drives) to the other frame (rear frame in an articulated hauler) is eliminated. Specific fuel consumption is expected to be greatly decreased due to the fact that much less parts rotate and generate drag and due to the fact that the machine can regenerate in overrun and braking conditions. Further, the kerb weight of the machine will be significantly less, due to the absence of the dropbox, propeller shafts and rear axles with final drives. This will of course lead to lower service cost and lower production cost.
Especially, an aspect of the invention creates conditions for eliminating the transmission shaft through the pivot joint between the front section and the rear section, which is a sensitive point subjected to high load during operation. Further, a steering angle between the front section and the rear section may be substantially increased due to that the pivot joint is free of any transmission shafts.
Further, elimination of the mechanical transmission to the other vehicle section sets a lot of space free for installation of energy storage means such a batteries.
Further, an aspect of the invention creates conditions for a more efficient packaging of the powertrain components in the first frame. For example, the weight distribution may be chosen in a much more favourable way than in a conventional articulated hauler. Especially, it would be advantageous to decrease the weight in the nose in front of the front wheel axle of a conventional articulated hauler. Therefore, the internal combustion engine is preferably positioned with its main extension direction transverse relative to a longitudinal direction of the work machine. Further, this design creates conditions for reducing the distance between the front wheels and the steering joint.
Further, this invention creates conditions for eliminating the gearbox and propeller shaft passing through between the operator and the front wheel axle in conventional articulated haulers. The operator position can therefore be lowered which will substantially decrease the impact of whole body vibrations in an x-direction (fore-to-aft) and a y-direction (sideways) of the operator.
According to a preferred embodiment, the power source comprises an electric machine for providing electric power. Preferably, the power source comprises means for generating mechanical power and the electric machine is operatively connected to the mechanical power generating means for converting the mechanical power to electric power. Especially, the means for generating mechanical power is constituted by an internal combustion engine and the electric machine forms a generator. Alternatively, the electric machine may be adapted to generate electric power directly (for example a fuel cell). According to a further alternative, the electric machine may be adapted to receive electric power from an external source, such as by plugging into a stationary power supply coupled to the power grid.
According to a further development of the last mentioned embodiment, the section with the mechanical power generating means comprises means for mechanical transmission of power from the mechanical power generating means to the ground engaging members of said section. Thus, the front wheels are directly mechanically driven, wherein the rear wheels are driven by the electric motor(s). This powertrain design creates conditions for an energy efficient operation, wherein the rear wheels are only driven in slippery conditions. Thus, in non-slippery conditions and conditions with limited slip, it may be sufficient to only drive the front wheels. Thus, prior art drag losses due to rotating powertrain parts in the rear section are eliminated.
Further, torque may be infinitely variably supplied to the rear wheels in order to support the front wheel drive in certain (slippery) conditions.
Preferably, the mechanical power transmission means comprises an axle adapted to drive a pair of said ground engaging members, wherein the axle comprises a differential gear adapted to transmit power to said pair of ground engaging members and a differential lock. The differential lock creates conditions for 100% lock in the front axle differential (which is not possible with Ackermann steering), which is essential when operating on slippery ground.
According to another preferred embodiment, the internal combustion engine is positioned with its main extension direction transverse relative to a longitudinal direction of the work machine. The internal combustion engine is preferably formed by a diesel engine with the cylinders in line, e.g. a straight engine. In this case, the main extension direction is in parallel with said straight line. According to an alternative, the engine's cylinders may be arranged in a V-shape, wherein the main extension direction is perpendicular relative to a plane defined by the V. This position of the internal combustion engine creates conditions for an efficient packaging of the powertrain components in the front section. Further, since the length of the nose of the articulated hauler can be significantly reduced, the visibility from the cab for an operator is significantly improved, especially when driving upwards a slope.
Further preferred embodiment and advantages thereof emerge from the description below, the figures and the claims.